Many peptide hormones, such as vasopressin and parathyroid hormone, stimulate adenylyl cyclase which results in an increase in cell cAMP content. CAMP, in turn, activates one or more protein kinases. It thus appeas that protein phosphorylation is an important step in the physiological response of a hormone. We are planning to study the role of protein phosphorylation at the level of hormone receptor-adenylyl cyclase interaction, protein kinase activation, and endogenous substrates which may be important in altering membrane transport characteristics. In this latter category, the components of microtubules and microfilaments will be a major focus of our attention.